The present invention generally relates to optical information storage units and laser power control methods, and more particularly to an optical information storage unit which uses a replaceable recording medium and to a laser power control method for controlling a laser power of a laser beam irradiated on a recording medium.
Recently, optical disks are regarded as possibly forming a core technology of the rapidly developing multimedia systems. In addition, there are demands to realize large storage capacities in the optical disks. For example, the maximum storage capacity of a recently proposed magneto-optical disk having a diameter of 3.5 inches is 640 MB. In such an optical disk having a large storage capacity, a beam spot of a light beam irradiated on the optical disk has an extremely small diameter, and a highly accurate tracking servo and laser power are required.
Generally, in the case of a storage unit which uses a replaceable recording medium, there exist mechanical errors of a recording medium loading process with respect to a spindle motor, and mechanical tolerances of a holding part which holds the loaded recording medium. In addition, the recording medium itself has physical inconsistencies and distortions in the shape thereof.
For this reason, there are cases where the recording medium is set obliquely with respect to an optical head. In such cases, the so-called tilt or skew is generated.
FIGS. 1A and 1B are diagrams showing an example of a conventional recording medium in a reproducing state. FIG. 2 is a diagram showing an example of a characteristic of a position of the recording medium with respect to a head position in the reproducing state of the recording medium.
FIG. 1A shows a perspective view of a recording medium 102. Further, FIG. 1B shows a state where the recording medium 102 is set obliquely with respect to an optical head 103. In this state, a recording surface of the recording medium 102 is not perpendicular but is inclined with respect to a rotary shaft 101 of a spindle motor 100.
When the recording medium 102 is rotated by the spindle motor 100 in the state shown in FIG. 1A and a beam spot 105 of a laser beam emitted from the optical head 103 scans a track 104 on the recording surface of the recording medium 102, a relationship between an optical axis of the laser beam emitted from the optical head 103 and an inclination of the surface of the recording medium 102 undergoes a sinusoidal change as shown in FIG. 2. In FIG. 2, the head position, that is, the optical axis of the laser beam emitted from the optical head 103, is indicated by a rotary angle in degrees.
FIGS. 3A and 3B are diagrams showing another example of the conventional recording medium in the reproducing state. FIG. 4 is a diagram showing an example of a characteristic of an inclination of the recording medium with respect to a head position in the reproducing state of the recording medium.
FIG. 3A shows a perspective view of a recording medium 110 which is generally deformed in a shape of an umbrella or an upside down bowl. Further, FIG. 3B shows a state where the recording medium 110 is set obliquely with respect to the optical head 103. In FIG. 3B, those parts which are the same as those corresponding parts in FIG. 1B are designated by the same reference numerals, and a description thereof will be omitted.
When the optical head 103 moves in a direction A2 in the state shown in FIG. 3B, a relationship between the optical axis of the laser beam emitted from the optical head 103 and the inclination of the recording surface of the recording medium 110 changes as shown in FIG. 4. In FIG. 4, the abscissa indicates the head position along the radial direction of the recording medium 110.
In the states shown in FIGS. 1B and 3B, the laser beam from the optical head does not reach the recording medium perpendicularly to the recording surface of the recording medium, and for this reason, an anticipated reflected light cannot be obtained. In other words, an anticipated laser power cannot be obtained due to a shape distortion of the beam spot.
When the anticipated laser power cannot be obtained, the effects caused thereby is small if the conditions such as the track pitch and the bit per inch (BPI) are not strict, that is, if the recording density is low. However, if the conditions such as the track pitch and the BPI are strict, that is, if the recording density is high, the effects caused by the reduced laser power are no longer negligible, and an error rate is increased thereby.
Therefore, methods of mechanically correcting the tilt or the skew by correcting the inclination of the spindle motor have been proposed.
But according to the methods of mechanically correcting the tilt or the skew by correcting the inclination of the spindle motor, there were problems in that a mechanical structure is required to control the inclination, and a space is required to accommodate this mechanical structure. In addition, there was another problem in that this mechanical structure cannot follow a high-speed rotation of the recording medium, since the spindle motor must be mechanically displaced.
Accordingly, it is a general object of the present invention to provide a novel and useful optical information storage unit in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an optical information storage unit which can obtain an optimum laser power regardless of the inclination of the recording medium, by controlling the laser power.
Still another object of the present invention is to provide an optical information storage unit which optically stores information on a disk shaped recording medium by irradiating a laser beam on the recording medium by a laser beam irradiating section, comprising a power control section controlling a laser power of the laser beam irradiated on the recording medium by the laser beam irradiating section depending on a rotary angle of the recording medium. According to the optical information storage unit of the present invention, the laser power can be controlled to an optimum value even if the laser beam is not perpendicularly incident to the recording medium, such as a case where the recording medium is loaded obliquely with respect to a rotary shaft, and it is therefore possible to accurately record and reproduce information with respect to the recording medium.
In the optical information storage unit, the power control section may control the laser power of the laser beam for each of blocks, where each of the blocks is made up of a predetermined number of sectors dividing a recording surface of the recording medium in a circumferential direction of the recording medium. In this case, it is possible to reduce the number of set values for the laser power, and the circuit scale of the optical information storage unit can be reduced.
In the optical information storage unit, wherein the power control section may control the laser power of the laser beam for each of zones dividing the recording surface of the recording medium in a radial direction of the recording medium. In this case, it is possible to appropriately control the laser power not only when the recording medium is inclined, but also when the recording medium is deformed.
In the optical information storage unit, the power control section may comprise a memory storing set values of the laser power for each region of the recording medium, and a power switching section reading the set value from the memory depending on a region of the recording medium irradiated by the laser beam, and switching the laser power of the laser beam emitted from the laser beam irradiating section based on the read set value. The memory may store, as the set values, offset values each of which is added to an initial value of the laser power when determining the laser power of the laser beam. In this case, it is possible to reduce the memory capacity required to store the set values in the memory, and the circuit scale of the optical information storage unit can be reduced.
The optical information storage unit may further comprise a section writing a test pattern on the recording medium and reading the test pattern from the recording medium, where the memory stores the set values depending on the test pattern read from the recording medium. In this case, it is possible to control the laser power for each individual recording medium which is loaded into the optical information storage unit, so that information can be read and written with respect to the recording medium under optimum conditions for the recording medium.
A further object of the present invention is to provide a laser power control method for controlling a laser power of a laser beam irradiated on a recording medium, comprising the steps of (a) controlling the laser power of the laser beam irradiated on the recording medium depending on a rotary angle of the recording medium. According to the laser power control method of the present invention, the laser power can be controlled to an optimum value even if the laser beam is not perpendicularly incident to the recording medium, such as a case where the recording medium is loaded obliquely with respect to a rotary shaft, and it is therefore possible to accurately record and reproduce information with respect to the recording medium.
In the laser power control method, the step (a) may control the laser power of the laser beam for each of sectors dividing a recording surface of the recording medium in a circumferential direction of the recording medium. In this case, it is possible to reduce the number of set values for the laser power, and the circuit scale of an optical information storage unit which employs the laser power control method can be reduced.
In the laser power control method, the step (a) may control the laser power of the laser beam for each of blocks, each of the blocks being made up of a predetermined number of sectors dividing a recording surface of the recording medium in a circumferential direction of the recording medium. In this case, it is possible to reduce the number of set values for the laser power, and the circuit scale of an optical information storage unit which employs the laser power control method can be reduced.
In the laser power control method, the step (a) may control the laser power of the laser beam for each of zones dividing a recording surface of the recording medium in a radial direction of the recording medium. In this case, it is possible to appropriately control the laser power not only when the recording medium is inclined, but also when the recording medium is deformed.
The laser power control method may further comprise the steps of (b) storing set values of the laser power in a memory for each region of the recording medium, and (c) reading the set value from the memory depending on a region of the recording medium irradiated by the laser beam, and switching the laser power of the laser beam depending on the read set value. In this case, it is possible to reduce the memory capacity required to store the set values in the memory, and the circuit scale of an optical information storage unit which employs the laser power control method can be reduced.
The laser power control method may further comprise the steps of (d) writing a test pattern on the recording medium and reading the test pattern from the recording medium, where the step (b) stores the set values depending on the test pattern read from the recording medium. In this case, it is possible to control the laser power for each individual recording medium which is loaded into an optical information storage unit which employs the laser power control method, so that information can be read and written with respect to the recording medium under optimum conditions for the recording medium.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.